Intriguingly, Lee, in a press release, said that Pinterest planned to make San Francisco's startup-heavy SoMa district its long-term home. But the company has only signed a short-term lease on its brand-new headquarters, 572 7th Street, according to Lee's statement.

That's curious, because 572 7th Street is adjacent to a larger property, 808 Brannan Street. Pinterest's new landlords, had been marketing the two buildings as a single property. Pinterest has reserved parking spots alongside 808 Brannan. And a sign on the front of 808 Brannan directs all deliveries to 572 7th Street.

Pinterest communications chief Barry Schnitt told us that the company is still finalizing its long-term plans but couldn't elaborate further. Chad Arkoff, a Flynn Holdings leasing agent who's been marketing the property, told us he couldn't comment on the property "in any capacity."

So we're left with a theory: Pinterest definitely doesn't need 55,000 square feet right now. But it could in relatively short order, having raised $100 million and started aggressively expanding its headcount. So it's likely secured 572 7th Street right away, and may be negotiating with Flynn over terms like whether it can sublease the rest of the property.

In any event, 808 Brannan Street isn't ready for anyone to move in yet, from what we saw over the weekend.